1. Field of the Invention
The present invention relates to a telecommunication system and, more particularly, to a multimedia broadcast/multicast service (MBMS) of a universal mobile telecommunications system (UMTS).
2. Discussion of the Related Art
A universal mobile telecommunications system (UMTS) is a third generation mobile communication system that has evolved from a standard known as Global System for Mobile communications (GSM). This standard is a European standard which aims to provide an improved mobile communication service based on a GSM core network and wideband code division multiple access (W-CDMA) technology.
It is noted that for the purpose of creating a specification for standardizing the UMTS, various organizations around the world including ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States and the TTA of Korea formed a Third Generation Partnership Project (3GPP). Many standard features of the UMTS are being adopted by 3GPP.
FIG. 1 illustrates an example of the construction of a general UMTS network.
As shown in FIG. 1, a UMTS includes a terminal (UE), a UMTS terrestrial radio access network (UTRAN) and a core network. The UTRAN includes one or more radio network sub-systems (RNS). Each RNS includes one radio network controller (RNC) and one or more Node Bs managed by the RNC. Each Node B, managed by the RNC, receives information sent by the physical layer of the terminal through an uplink, and transmits data to the terminal (UE) through a downlink. Thus, Node B's operate as access points of the UTRAN for the terminal.
A primary function of the UTRAN is to constitute and maintain a radio access bearer (RAB) for a communication between the terminal and the core network. The core network applies requirements for a quality of service of an end-to-end to the RAB, and the RAB supports the QoS requirement the core network 130 sets.
Accordingly, by constituting and maintaining the RAB, the UTRAN can satisfy the QoS requirement of the end-to-end. The RAB service can be divided into lower Iu Bearer service and Radio Bearer service. The Iu Bearer service handles a reliable transmission of a user data in the boundary node between the UTRAN and the core network, while the radio bearer service handles a reliable transmission of a user data between the terminal and the UTRAN.
FIG. 2 shows a structure of a radio protocol between a terminal which operates based on a 3GPP RAN specification and a UTRAN. The radio protocol is horizontally formed of a physical layer (PHY), a data link layer, and a network layer and is vertically divided into a control plane for transmitting a control information and a user plane for transmitting data information. The user plane is a region to which traffic information of a user such as voice or an IP packet is transmitted. The control plane is a region to which control information such as an interface of a network or maintenance and management of a call is transmitted.
In FIG. 2, protocol layers can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on three lower layers of an open system interconnection (OSI) standard model well known in a communication system. Each layer of FIG. 2 will now be described.
The first layer (L1) provides information transfer service to an upper layer by using various radio transmission techniques. It is connected to an MAC (Medium Access Control) layer at the upper position through a transport channel, and data between the MAC layer and a physical layer are moved through the transport channel.
The MAC provides assignment service of an MAC parameter for assigning and re-assigning a radio resource. It is connected to a radio link control layer, an upper layer, by a logical channel, and various logical channels are provided according to the kind of transmitted information. In general, when information of the control plane is transmitted, a control channel is used. When information of the user plane is transmitted, a traffic channel is used.
The MAC is classified into MAC-b sublayer, MAC-d sublayer and MAC-c/sh sublayer according to the type of transport channel it manages. The MAC-b sublayer manages a broadcast channel (BCH), a transport channel handling broadcast of system information. The MAC-c/sh sublayer manages a common or shared transport channel such as the FACH or a DSCH (Downlink Shared Channel) shared by multiple terminals.
In the UTRAN, the MAC-c/sh sublayer is positioned in the CRNC. Since the MAC-c/sh sublayer manages channels shared by every terminal in a cell, one MAC-c/sh sublayer exists in each cell. The MAC-d sublayer manages a dedicated channel (DCH), a dedicated transport channel for a specific terminal. Therefore, the MAC-d sublayer is positioned at the SRNC handling management of a corresponding terminal and one MAC-d sublayer exists in each terminal.
The RLC layer supports reliable data transmission and performs a function of segmentation and concatenation of RLC service data unit (SDU) coming down from an upper layer.
The RLC SDU delivered from the upper layer is adjusted in its size suitable for a processing capacity in the RLC layer, to which header information is added and transmitted as a protocol data unit form to the MAC layer. The RLC layer has an RLC buffer to store RLC SDU or PDUs coming down from the upper layer.
A broadcast/multicast control (BMC) layer schedules a cell broadcast (CB) message delivered from the core network and allows user equipments positioned in a specific cell to perform a broadcast function.
At the side of the UTRAN, the CB message delivered from the upper layer is added with information such as a message ID, a serial number or a coding scheme and transmitted as the BMC message form to the RLC layer, and transmitted to the MAC layer through the logical channel CTCH (Common Traffic Channel). The logical channel CTCH is mapped with the transport channel FACH and S-CCPCH.
A packet data convergence protocol (PDCP) layer is positioned at an upper side of the RLC layer and allows data to be transmitted through a network protocol such as an IPv4 or IPv6 to be effectively transmitted on the radio Interface with a relatively small bandwidth. For this purpose, the PDCP layer performs a function of reducing unnecessary control information, which is called a header compression, and RFC2507 and RFC3095, a header compression technique defined in an Internet standardization group called IETF (Internet Engineering Task Force). With these methods, because the header part is allowed to transmit only essential information, less control information is transmitted, thereby reducing a quantity of data to be transmitted.
The radio resource control (RRC) layer positioned in the lowest portion of the L3 is defined only in the control plane and controls the logical channels, the transport channels, and the physical channels in relation to the setup, the reconfiguration, and the release of the RBs. The RB is a service provided by the second layer for data transmission between the terminal and the UTRAN. Setting up the RB means processes of stipulating the characteristics of a protocol layer and a channel, which are required for providing a specific service, and setting the respective detailed parameters and operation methods.
The multimedia broadcast/multicast service (MBMS) will now be described.
The MBMS is a service transmitting multimedia data such as an audio, a video or an image to a plurality of terminals by using a uni-directional point-to-multipoint bearer service. UTRAN transmits the MBMS data over a downlink common transport channel such as FACH or DSCH in order to heighten an efficiency of a radio network.
The MBMS has two types of modes of a broadcast mode and a multicast mode. Namely, the MBMS service is divided into an MBMS broadcast service and an MBMS multicast service.
The MBMS broadcast mode is a service transmitting multimedia data to every user located in a broadcast area. The broadcast area herein refers to an area where a broadcast service is available. One or more broadcast areas can exist in one public land mobile network (PLMN), and one or more broadcast services can be provided in one broadcast area. Further, one broadcast service can be provided to several broadcast areas.
The MBMS multicast mode is a service for transmitting multimedia data only to a specific user group in a multicast area. Here, the multicast area refers to an area where a multicast service is available. There can exist one or more multicast areas in one PLMN, and one or more multicast services can be provided in one multicast area. Further, one multicast service can be provided to several multicast areas.
In the MBMS multicast mode, a user is required to join a multicast group for receiving a specific multicast service. Here, the multicast group refers to a user group receiving a specific multicast service, and joining herein refers to a behavior of joining to the multicast group for receiving the specific multicast service.
The radio network temporary identifier (RNTI) will now be described.
The RNTI is used as identification information of a terminal while connection is maintained between the terminal and the UTRAN, including S-RNTI, D-RNTI, C-RNTI and U-RNTI.
S-RNTI (Serving RNC RNTI) is assigned by an SRNC (Serving RNC) when a connection is set up between the terminal and the UTRAN, and used as base information for the SRNC to identify a terminal.
D-RNTI (Drift RNTI) is assigned by a DRNC (Drift RNC) when a handover occurs between radio network controllers according to a terminal's movement.
C-RNTI (Cell RNTI) is used as information to identify a terminal in an CRNC (Controlling RNC) and given a new C-RNTI value from the CRNC when a terminal enters a new cell.
U-RNTI (UTRAN RNTI) consists of an SRNC identity and an S-RNTI and provides absolute identification information of a terminal in case that identification information of an SRNC managing a terminal and identification information of a terminal in the corresponding terminal can not be recognized.
When data is transmitted by using a common transport channel, an MAC-c/sh layer includes C-RNTI or U-RNTI in a header of an MAC PDU and transmits it. At this time, the header of the MAC PDU also includes a UE ID type indicator informing a type of the RNTI.
One or more physical channel S-CCPCH (Secondary Common Control Physical Channel) can be provided by a cell, so that a terminal desires to receive a transmission channel FACH (Forward Access Channel) or a PCH (Paging Channel), it first selects a mapped S-CCPCH channel. That is, the terminal selects a S-CCPCH channel to be received by itself by using the U-RNTI.
The conventional RNTIs are used only for the point-to-point radio service, they serve to identify only one terminal. Thus, when the terminal receives data through the downlink common transport channel, it recognizes whether the RNTI included in the header of the MAC PDU is the same as an RNTI assigned to itself and transfers only data including the same RNTI.
However, the MBMS transmitting data to a plurality of terminal, that is, to a terminal group, by using the point-to-multipoint radio service on the radio, the conventional RNTI can not be used.
First, when the conventional RNTI is used for the common transport channel for the MBMS, RNTIs of plural terminals for receiving a corresponding data should be all included in the header of the MAC PDU. Then, RNTIs as many as the receiving terminals are included in the header of the MAC PDU, the header becomes fat.
For this reason, in case of the conventional CBS service, no RNTI is included in the header of the MAC PDU to provide the point-to-multipoint radio service. Instead, a message ID is included in a BMC message in an BMC layer. In this case, however, the MAC layer of the terminal can not recognize whether a received data belongs to itself, every data received over the common transport channel should be transmitted to the upper RLC and BMC layers.
There is another disadvantage of the message identifier. In the conventional art, the user gives the BMC layer message identifier information to be received. The terminal thereby transfers a corresponding message to the upper layer only when a message identifier of the received BMC message is identical to a message identifier selected by the user. With this method, protection of information of a specific message data is not guaranteed. That is, because the whole message identifiers are known to the every user, it is not possible that a specific message data is received only by a specific user group or a specific message data is protected from damage or distortion.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.